1. Field of the Invention
The present invention relates to an uninterruptible power supply.
2. Description of the Related Art
In an external power supply for converting the electricity of a commercial power source to electrical power having a predetermined voltage to supply the power to electronic equipment, the voltage of the electrical power supplied to the electronic equipment temporarily drops if an instantaneous power failure occurs in the commercial power source, thus possibly causing problems with the operation of the electronic equipment. For this reason, there has been a publicly-known uninterruptible power supply used to detect the instantaneous power failure in the commercial power source by a power failure detection signal output by the external power supply and supply electrical power from a backup battery or the like to the electronic equipment in case of an instantaneous power failure.
In general, a comparatively long time lag from the time an instantaneous power failure occurs to the time the external power supply outputs a power failure detection signal is in many cases associated with a general-purpose power failure detection circuit included in the external power supply as a standard feature. In addition, a conventional uninterruptible power supply starts up a converter circuit, an inverter circuit, and the like included therein only after detecting the power failure detection signal. This means that a certain period of time is required until the uninterruptible power supply is ready to supply electrical power having a rated voltage, from the time the power failure detection signal is detected. Accordingly, the uninterruptible power supply may fail to back up in time if electrical power supply from the commercial power source to the external power supply stops due to the instantaneous power failure, though there is more or less the time difference from when the instantaneous power failure occurs to when the output voltage of the external power supply drops. Consequently, the voltage of electrical power supplied to the electronic equipment may drop temporarily.
As a related art intended to solve such problems as described above, there has been publicly known a power failure detector or the like for rapidly detecting an instantaneous power failure in a commercial power source (see Japanese Patent Laid-Open Nos. 10-19943, 2001-13175, 2006-126135, and 2007-225427).
The power failure detector for rapidly detecting the instantaneous power failure in the commercial power source is generally complex in configuration and large in scale and requires great amounts of cost and time for development, however. The power failure detector is thus extremely expensive in many cases.
An object of the present invention, which has been accomplished in view of such circumstances as described above, is to provide an uninterruptible power supply, at low cost, in which the voltage of electrical power supplied to electronic equipment is less likely to drop temporarily even if an instantaneous power failure occurs in a commercial power source.